I've been punting since 2002 but only taking Sildenafil since around 2012.
During the first 10 years I experienced much greater difficulty reaching orgasm when punting in hot weather and non-a/c rooms.
Now I am on the pill (normally 50mg, sometimes 100mg) I still often find that hot weather inhibits orgasm although the erection sustaining effects are still present.
I can't comment on whether keeping the pills in too hot conditions renders them less effective because I just don't know.
But what I experience is that with or without the chemical aforementioned, a happy ending, for me at least, is in cooler seasons more frequently.